The state of the art includes a device to form spirals wherein a curved element is arranged inside a containing cylinder, in which the spirals are formed and accumulate, and is kept substantially parallel to the inner surface of the containing cylinder.
In this device, while the containing cylinder is made to rotate, the curved element is made to gradually advance, parallel to the axis of rotation of the cylinder, and is removed from inside the coil when the latter has been completed.
Although this device facilitates the formation of the spirals of the coil, it does not ensure that a compact coil is formed, since the reciprocal movement of the spiralforming tool and the containing cylinder is quite uncontrolled and since the stock which is being coiled is not subjected to a controlled tension.
The U.S. Pat. No. 4,664,329 discloses a coiler to wind a wire around a central mandrel which is rotated by means of a belt contacting the mandrel outer surface and disposed around a plurality of pulleys, one of which is connected to a motor. In this device the wire to be wound is horizontally moved by a first traverse assembly mounted slidable on fixed bars parallel to the rotational axis of the mandrel and is vertically moved by a plate connected to an actuator and independent from the traverse assembly. On such a plate is also mounted one of the pulleys which control the movement of the belt. This device has the disadvantage that the wire to be wound arrives in the proximity of the mandrel not always perpendicular to the rotational axis of the mandrel, but with an inclination which is more or less accentuated in accordance with the position of the traverse assembly with respect to the mandrel; consequently the different coils on a same layer are not uniformly distributed.
The present applicant has designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to obtain further advantages.